The present invention relates to a robot control system and, more particularly, to a robot control system which makes it possible to grip a workpiece without fail even if the work is somewhat offset from the correct position, and which permits easy teaching for gripping and stacking of workpieces on a work table.
Playback-type industrial robots have been put into practical use and are fully exhibiting their ability, well satisfying the demand for saving labor and procedural simplification of work in view of the current rise in labor costs. Particularly, in machine factories in which many machine tools are installed, a remarkable effect has been achived by employing the playback type industrial robot for simple services such as exchange of workpieces, exchange of tools and so forth for each of the machine tools. Under these circumstances, the demand for the playback type industrial robot is increasing year by year.
In the actual use of the playback type industrial robot, instructions for the services to be performed by the robot are applied beforehand to the robot through a teaching box and the content of the instructions (referred to as "robot command data" hereinafter) is stored in a memory incorporated in the controller. A series of robot command data is read each time the service demand is raised by the machine to make the robot serve the respective machine.
The robot command data is composed of the information concerning the point to be serviced, operation speed, and a service code which commands control of the service hand at the point, exchange of signals between the machine and the control system and so forth. The above-mentioned teaching generally includes the following steps: namely, (1) setting a memory address where the robot data is to be stored, (2) positioning by a jog feed (manual feed), (3) setting of point position information and speed command and (4) setting of robot service code. The instruction for a series of robot services are made by repeating the sequence including the above-mentioned steps (1) to (4). Therefore, the robot performs correctly and successively various tasks such as exchange of workpieces, removal of metal scraps, exchange of tools, control of the hand and so forth, after completion of positioning at a predetermined speed, in accordance with the robot command data each time the service demand is issued, unless any impediment exists in the mechanical portion.
If a workpiece is positioned at a slight offset from the correct position, the hand cannot grip the workpiece securely even it it is moved correctly to the commanded position as instructed. In a case where a multiplicity of unmachined workpieces are stacked on the work table, the position of gripping varies depending on the size, dimensions, etc. of the workpiece, so that it is necessary to take the trouble of renewing the position command each time a workpiece is gripped. When the machined workpieces are stacked, the position at which the hand releases the workpieces varies depending on the desired location of workpiece, so that it becomes necessary to take the trouble of renewing the position command for releasing the workpiece each time the release takes place.